1. Field of the Invention
This invention relates to a medical branch tube. More particularly, it relates to a medical branch tube having a closure which normally blocks the flow path of the branch tube, but is breakable to open the flow path.
2. Prior Art
Plasmapheresis therapy uses tubing systems including a plurality of sections of tubing connected through a branch tube. In most systems, a plurality of flow paths are not used at the same time and a particular set of flow paths are used at one time. A certain flow path which is not in use must be blocked by a plug at an appropriate intermediate location until the time when it is desired to pass blood therethrough. It is necessary upon use that the plug can be readily broken to open the flow path.
A prior art flow path plug used in a branch tube is described by referring to FIG. 4. The branch tube includes a main tube 1. The flow path plug mounted in the main tube 1 includes an annular base 8 joined to the inner wall of the main tube by adhesive bonding or heat welding. A closure member 9 is integrated to one end of the base 8 to block the main tube flow path, but spaced apart from the inner wall of the main tube 1. A notch or thin-walled portion 10 is provided at the interface between the base 8 and the closure member 9. The plug normally blocks the flow path of the main tube. When it is desired to open the flow path, the closure member 9 is broken at the thin-walled portion 10 and removed from the base 8.
The branch tube of the above illustrated structure, however, has several drawbacks.
(1) The plug has the base 8, the closure member 9, and the thin-walled portion 10 therebetween. After the thin-walled portion 10 is broken to remove the closure member 9 from the base 8 to open the flow path, the base 8 is left on the inner wall of the main tube 1. Since the base 8 is affixed to the inner wall of the main tube 1, that is, the base 8 is a separate member from the main tube 1, there is essentially formed a step 22 between the end of the base and the main tube. The step 22 remains on the main tube inner wall even after the closure member 9 is broken and removed. Then the step 22 forms an obstacle against the flow of fluid, typically blood, to prevent smooth passage of fluid because the fluid would stagnate or become turbulent at the step 22.
(2) The step 22 causes turbulent flow of blood, which stimulates and facilitates clotting of blood.
(3) When the closure member 9 is broken and removed at the thin-walled portion 10, the main tube 1 is likely to bend at the step 22 because the base 8 is secured to the main tube inner wall. Folding of the main tube renders it difficult to tear off the closure member 9 at the thin-walled portion 10 between the base 8 and the closure member 9.
(4) The presence of the base 8 extends the flow path of the main tube upstream of the plug by the length of the base. When the branch tube is used in plasmapheresis therapy, the volume of blood entering the dead flow path of the main tube which is not yet on use is increased by the volume of the base 8. Such an extra volume of blood in a dead cavity increases the risk that blood would stagnate and clot to eventually block the flow path.